As known, hadrontherapy is the therapeutic technique that uses beams either of protons or heavier charged particles with mass number higher than 1.
It is equally known that in protontherapy, that is that particular hadrontherapy technique based on the use of proton beams, therapeutic beams of relatively low current (of the order of some nanoamperes) are used, with energies in the range 60 to 250 MeV, and a velocity interval between about 25% and 62% of the velocity of light.
It is also observed that in the case of different ions, therapeutic beams with lower currents and higher energies are required compared to the ones for the protons. For example, in the case of carbon ions 12C6+, the required energies are between about 1.500 and 4.800 MeV (about 120 e 400 MeV/u). For a generic ion the interesting energies are from 50 to 500 MeV/u, corresponding to velocities between 15% and 75% of the velocity of light.
In the field of protontherapy among the different types of existing accelerators both cyclotrons (conventional or superconducting) and synchrotrons are used. The use of linear accelerators (Linac) has also been proposed.
The mass of the cyclotron magnet increases with the mass number and with the energy of the accelerated ions and becomes very large when one intends to cover the whole range of the energies needed for the therapy with carbon and similar ions. In particular today there are no hadrontherapy hospital centers based on cyclotrons accelerating carbon ions to the maximum energy of about 5000 MeV. Therefore special synchrotrons are used, adjusted for such a therapy and, unlike the cyclotrons, they have the extra advantage of producing variable energy ion beams.
However, hadrontherapy centers equipped with a synchrotron are extremely complex as they require a high number of high technology equipments derived from the technology of particle accelerators. In addition these centers are quite large, also due to the surface occupied by the synchrotron, and they require high investments and large installation surfaces that are not always available in the hospitals neighborhoods.
It is also acknowledged that the most advanced radiotherapy requires beams of composite charged particles (either totally or partially ionized nuclei or molecules) with mass number greater than 1, of quite low intensity (less than a few nanoampere). Such a requirement does not hold in the in the field of particle accelerators; physicists indeed need high currents for their experiments. This simplification, typical of the medical use, adds up to the requirement for the highest possible compactness of the system, as it ought to be installed in a hospital environment.